Belt Design Question

I am attempting to design a basic 3 axis system, where the motor to idler ratio is 3:1, and the idler to driven ratio is 1:2. The motor is 1.5 kW, variable speed. All three axis are in vertical alignment. This is a belt drive using a flat multi-vee belt.
My problem is trying to explain the difference between the static and dynamic loads on the shafts. I have been told that centrifugal force plays a part in the lower dynamic loads, but I am still not able to understand this to a point where I can pass along the information. The motor will rotate anywhere from 150 to 10000 RPM - how does such a low speed generate enough centrifugal force to change the shaft load?

Can anyone pass on some basic theory or point me to some sites where I can read up on this?

I am assuming that you are referring to rotary bearings when talking about centrifugals. Either way, a bearing has a dynamic load capacity which is the maximum load it can handle while still rotating. This is opposed to the static load which is the max load while the bearing is not rotating.

I didn't see anything that would provide an answer as to why a rotating shaft would see lower loads than a stationary shaft. I realize the bearings will distribute the load - that isn't where my problem lies. I just need to nderstand the basic theory behind why a dynamic load is lower than a static load.